In an embodiment, the invention provides a structure of MEMS microphone includes a substrate of semiconductor, having a first opening in the substrate. A dielectric layer is disposed on the substrate, having a dielectric opening. A diaphragm is within the dielectric opening and held by the dielectric layer at a peripheral region, wherein the diaphragm has a diaphragm opening. A back-plate is disposed on the dielectric layer, over the diaphragm. A protruding structure is disposed on the back-plate, protruding toward the diaphragm. At least one air valve plate is affixed on an end of the protruding structure within the diaphragm opening of the diaphragm. The air valve plate is activated when suffering an air flow with a pressure.